1. Field of the Invention
This invention relates to the preparation of an organopolysiloxane composition and more particularly, to a process for preparing a room temperature organopolysiloxane composition which is useful as a construction sealant as having good working or laying properties.
2. Description of the Prior Art
As is known in the art, it is usual to fill, with sealants, joint portions such as of concrete blocks and sash window frames and also marginal portions of glass window in various building structures. Examples of the sealant include those made of silicone resins, polysulfites, polyurethanes, acrylic resins, SBR, butyl rubbers or resins and the like. Especially, silicone sealants have been predominantly employed in the fields wherein good bonding properties, heat resistance, weatherability and durability are highly required.
Silicone sealants are usually used such that a composition filled in a cartridge is applied to joint portions and is surface-finished such as with a spatula prior to curing of the composition. For this purpose, the sealant should have non-fluidity and good laying properties.
In order to meet the above requirement, silica fillers are added to the composition at a high filling rate. This presents several problems that the addition of the filler does not proceed smoothly and that the physical properties of the resultant silicone rubber after curing lower.
Japanese Patent Publication No. 39-22438 proposes a silicone rubber composition to which boric acid or alkyl borates are added in order to impart non-sagging properties to the composition. This composition has the problems that when the composition is not thermally treated, satisfactory results are not obtained and a curing reaction is impeded by the addition.
Japanese Patent Publication No. 49-5510 proposes the addition of organic liquids whose vapor pressure is higher than a predetermined level, to a composition comprised of a liquid organopolysiloxane and hydrophobic silica. The organic liquid is inconveniently flammable and volatile, coupled with another problem of toxicity.
In order to improve fluidity, there have been proposed the addition of a polyether compound to a silicone rubber composition (Japanese Laid-open Patent Application No. 56-853) and the addition of a reaction product of a polyether compound and a functional silane to a silicone rubber composition (Japanese Laid-open Patent Application No. 62-135560). Although the addition of the polyether compound or the reaction product is, more or less, effective in improving the fluidity of silicone rubber compositions, a problem commonly arises in that these compositions are poor in working properties. Especially, when subjected to surface finishing with a spatula, the composition sticks on the spatula and is liable to string or rope, thus being difficult to release from the spatula.
Japanese Laid-open Patent Application No. 2-41361 proposes a method wherein non-sagging properties are imparted to a composition without use of any additives. This composition has the problem that cracking is apt to occur in the surfaces thereof on the way of curing of the composition.